Write a program in java that reverses a String without using any libraries that contain a built-in reverse() function.

Answer 1

The previous solution given will work! I'm going to suggest some modifications. Here's the original:

public static String reverse(String str) {

String reversed = "";

for (int i = str.length() - 1; i >= 0; i--) {

reversed += str.substring(i, i + 1);

}

return reversed;

}

That call to str.substring(i, i + 1) is essentially a way of picking out a single character at index i, but there's actually a built in String method for that: charAt. And I think things read a bit more easily using it. Using it is also a bit semantically clearer in my opinion (others can disagree!):

public static String reverse(String str) {

String reversed = "";

for (int i = str.length() - 1; i >= 0; i--) {

reversed += str.charAt(i);

}

return reversed;

}

It's generally better to use a StringBuilder, though, since that keeps us from generating a lot of Strings along the way (what if our input String was a very long String)?

public static String reverse(String str) {

StringBuilder reversed = new StringBuilder();

for (int i = 0; i < str.length(); ++i) {

reversed.insert(0, str.charAt(i));

}

return reversed.toString();

}

Note that here, I actually iterated forward through the String and prepended (using insert), but you could iterate backwards and use the append method, too. But the main point is that using a StringBuilder keeps us from having to generate new Strings for each character in the input.

I hope that helps!

Answer 2

We can't use a pre-defined function in java that can instantaneously reverse a string. Therefore, we must come up with a way to do so. One way we can do this is by creating a new string adding individual characters to it by traversing through the original string in reverse order. This will result in the final string being the reverse of the original string, and this will be our solution to the problem. An implementation of this solution looks like:

public class MyClass {

public static void main(String args[]) {

String before="hello";

String after=reverse(before);

System.out.println(after);

}

public static String reverse(String str){

String reversed="";

for(int i=str.length()-1; i>=0; i--){

reversed+=str.substring(i,i+1);

}

return reversed;

}

}